1. Field of the Invention
The present invention relates to the separation of benzene and cyclohexane and, more particularly, to the use of distillation in the presence of selected nitriles to obtain a stream enriched in benzene relative to the initial stream as the tails from the distillation and a stream enriched in cyclohexane relative to the initial stream as the heads from the distillation.
2. Description of the Prior Art
Numerous processes have been suggested for separating hydrocarbons having similar boiling points including chemical processes, highly efficient fractional distillation, azeotropic distillation and solvent extraction both in the liquid and vapor phase, Technique of Organic Chemistry, IV, "Distillation" Rose et al, Interscience Publishers, Inc. N.Y. (1951). Glycols and sulfolanes are the most common solvents although methylglutaronitrile is alleged to be extremely efficient, "Refining Petroleum for Chemicals" ACS Monograph No. 97, Chap. 15, 1971.
U.s. Pat. No. 2,441,827 issued on May 18, 1948 discloses a process for the separation of relatively olefinic hydrocarbons from relatively nonolefinic hydrocarbons which employs a large class of nitriles to selectively dissolve at least one of the hydrocarbons of the hydrocarbon mixture without dissolving substantial quantities of the other hydrocarbon or hydrocarbons in the mixture. The patentee discloses that the extraction process may be conducted in a liquid phase by thoroughly mixing an appropriate amount of the nitrile with the hydrocarbon mixture, allowing the mixture to separate into two liquid phases and separating the two phases by decantation. An alternate method for practicing the process is to effect the solvent extraction in the vapor phase by contacting the mixture of hydrocarbons in a fractionating column with the liquid solvent to permit scrubbing of the vapors by the solvent whereupon the soluble hydrocarbon is removed from the vapor phase by the solvent and passes downwardly to the base of the column. The Patentee discloses that if it is desired to vaporize the mixture, the solvent should condense before the hydrocarbon so that the liquid solvent can then contact the hydrocarbon vapors and solubilize at least one of the components.